S.. L. Penfield — Beryllium Minerals from Colorado. 489 



prism «'-§, 2130 may be observed. The most interesting 

 feature of the crystals is that, while the material of the beryl 

 is perfectly fresh and transparent, the crystals have been 

 attacked by some solvent and partially dissolved away with 

 the formation of very prominent etchings. The extent to 

 which the crystals have been etched, varies much in the 

 different specimens, while the character of the etching, com- 

 mon to all the crystals, is that the beryl substance is eaten 

 away so as to leave steep pyramidal forms. In all cases there 

 is left, not one single steejD pyramid, but a number of them 

 grouped together in parallel position. The action of the sol- 

 vent has been most energetic at the ends of the crystals. 

 Frequently the whole top of a crystal will be eaten away 

 leaving a very irregular termination composed of groups of 

 fine needles sometimes massed together in a deep depression 

 at the end of a crystal ; or some of the basal plane will still be 

 intact, reflecting the light perfectly, while deep pits will be 

 eaten into it, the Walls of which represent the sides of the steep 

 pyramids. Again the solvent action seems to have started 

 somewhere along the sides of the prism when a cavity will be 

 eaten into the crystal, sometimes nearly or quite through it, 

 into which the little pyramidal points project. Again the 

 crystals have been almost completely removed from the matrix 

 leaving a hexagonal cavity containing a little cluster of fine 

 beryl needles. If the action has been less prolonged or energetic 

 the etching appears as simple elongated depressions eaten into 

 the prismatic faces. 



The steep beryl pyramids, which are seldom 4 mm in length, 

 usually have faces and edges which are somewhat rounded 

 so that they appear like needle points, and it was some time 

 before one was obtained which would give in any way satis- 

 factory reflections on the goniometer. At last one was obtained 

 where the needles were unusually large and distinct, and 

 yielded faint reflections which were measured on a horizontal 

 Fuess goniometer, with the lowest ocular, combination d of 

 Websky.* The most prominent reflections, which occurred 

 twelve times in a complete revolution of the crystal, were 

 from the faces of a dihexagonal pyramid and yielded the 

 following supplement angles, the smaller alternating with the 

 larger: 12°, 47^°, 12|°, 47°, 12^°, 46°, 13°, 46|°, 13°, 46|°, 

 12^°, 46^°. On close examination it was found that the ob- 

 tuse angle was above the edge of the unit prism, the two faces 

 making this angle appearing like one face of a pyramid of the 

 second order, for which the steep pyramids were at first taken. 

 Calculating from the average of the angles given above 12° 30' 

 and 46° 40' we find that this pyramid has the symbol 12-f, 

 36"24-60 - 5. The obtuse and acute angles obtained by calcu- 



*Zeitsch. Kryst., iv, p. 550. 

 Am. Jour. Sci. — Third Series, Vol. XL, No. 240. — Dec, 1890. 

 31 



